With the gradual depletion of the richer ore deposits, the recovery of valuable metals and metal products from lowgrade ores and from the tailings of mining and processing operations becomes increasingly important. To permit the efficient extraction of metals from these sources, improved recovery means are urgently needed. The present invention falls within this category, providing an improved method for extracting finely divided metallic copper and/or cuprous oxide from copper precipitate or "cement copper" or any other copper bearing material.
For many years the copper mining industry has produced a low-grade byproduct known as copper precipitate or "cement copper". Cement copper is derived from relatively weak aqueous solutions of copper salts, notably copper sulfate. Such weak solutions of copper salts can be prepared by percolating large quantities of weak sulfuric acid over massive beds of low-grade copper oxide ore. Alternatively, such solutions may be obtained by pumping underground water from copper mines, from spent pickle liquors in brass and copper mills, and in various other operations.
To prepare the copper precipitate or "cement copper," the weak copper-bearing solutions are contacted in large tanks or water storage and distribution vessels with scrap iron. The scrap iron is usually shreddled cans or other iron or steel wastes from metal-working and manufacturing operations.
Copper is precipitated from the weak copper sulfate solution according to the following equation: EQU CuSO.sub.4 + Fe .fwdarw. FeSO.sub.4 + Cu
The resultant fine copper precipitate sludge or "cement copper" is heavily contaminated with iron and contains substantial amounts of other impurities such as carbonaceous materials, base metals and basic metallic salts, etc. In a typical case, the cement copper will average upwards of 60 percent to 85 percent copper. For example, a typical cement copper, after removal from the precipitation tanks, exhibits the following characteristics:
TABLE A ______________________________________ Screen Percent Size Weight Impurities ______________________________________ +65 6.1 Acid insolubles 2.7 +100 1.6 Ammonia insolubles 4.3 +200 3.4 Copper content 81.5 +325 7.6 -325 81.3 ______________________________________
Cement copper particles are dendritic, a characteristic that imparts a distinct advantage in the field of powder metallurgy as the particles tend to bind together when subjected to high pressures. This advantage is offset, however, by the presence of many impurities in cement copper which render the material unsuitable for direct use in powder metallurgy and related fields.
Consequently, cement copper has not generally been regarded as suitable for semi-direct conversion to valuable copper products by purely chemical methods. Rather, cement copper was ordinarily introduced into the pyrometallurgical copper smelting process, either at the reverberatory furnace or the converting stage. In one instance, cement copper was converted to useful copper products by dissolving the cement copper in sulfuric acid followed by electrolysis of the copper sulfate. More recently, cement copper was dissolved in the sulfuric acid and the resulting copper sulfate was catalytically reduced at elevated pressure with hydrogen. However, such electrolytic or catalytic reduction processes do not favorably compare with chemical purification procedures because of cost and complexity of the operations.
Recently, however, certain chemical processes have been proposed for the separation of cuprous oxide and metallic copper from copper precipitate.
Cuprous oxide Cu.sub.2 O is a dark red or carmine-red crystal or powder which is used in the production of copper salts, in ceramics, and for the development of porcelain red glaze and red glass. It is important in electroplating and in antifouling paints. It is also of value in agriculture as a seed treatment material to control seed-borne and soil-borne disease organisms, and although other compounds may be used, it is still the best fungicide for certain crop seed treatments, and has gained recent acceptance as a fungicide on citrus fruits.
Metallic copper is recently in great demand in the electronics industry where it is employed as a conductive coating over a ceramic substrate. Very finely divided particles of high-purity copper are required for this application. Copper in this form is most readily obtained by chemical precipitation.